Not one of the transformers that I know, but a Decepticon just the same. It is worth taking a look at how the author constructed the helmet. An outstanding result overall, even though it does not transform http://www.instructables.com/id/Transformers-Soundwave-Costume/
A well-documented (with still photos) non-transformable adult Optimus Prime costume. If I were building a constume, I would pay attention to his travails. Still, the result is a little too boxy for my taste. http://optimuscostume.blogspot.com/
Sae found this webpage, depicting a nice transformable Optimus Prime costume.
http://gizmodo.com/263917/real+life-transforming-optimus-primer-costume
Detailed step-by-step instructions on how to build a non-transforming G1 Optimus Prime costume. http://www.instructables.com/id/Building-Optimus-Prime/
Poor instructions with photos on how to use foam from $10 camping mats to make an Optimus Prime costume. http://www.instructables.com/id/Optimus-Prime-from-1000-foam-camping-mats/
Not one of the transformers that I know, but a Decepticon just the same. It is worth taking a look at how the author constructed the helmet. An outstanding result overall, even though it does not transform http://www.instructables.com/id/Transformers-Soundwave-Costume/
Here are 21 transformer costume "plans" with accompanying photos. Check out #19. http://www.coolest-homemade-costumes.com/halloween-costume.html
A very general plan to make an Optimus Prime costume with no photos. Still, there are a couple of decent ideas thrown in there. http://www.associatedcontent.com/article/2121005/transformers_optimus_prime_halloween.html?cat=74
A well-documented (with still photos) non-transformable adult Optimus Prime costume. If I were building a constume, I would pay attention to his travails. Still, the result is a little too boxy for my taste. http://optimuscostume.blogspot.com/